SCH39166 is a selective antagonist of dopamine D1 and D5 receptors. Dopamine neurotransmission is stimulated by all addictive drugs and even highly palatable food. But the addictive properties of drugs such as cocaine, nicotine, opiates and ethanol appear to be associated with dopamine stimulation of D1 and/or D5 receptors. Since SCH39166 is extensively glucuronidated in humans, it is clinically relevant to study the effects of various degrees of altered hepatic function on the pharmacokinetics of the drug -- especially in light of the prevalence of hepatic disease in substance-addicted persons. The primary objective of this single dose study is to evaluate and compare the pharmacokinetics of SCH39166 in subjects with normal liver function and with various degrees of stable chronic liver disease. Data from this study will be used to develop dosing guidelines for patients with various degrees of chronic liver disease.